Charge coupled device (CCD) image sensors and complementary metal oxide semiconductor (CMOS) image sensors are often used in imaging devices, such as, digital cameras and digital video recorders, as image pick up apparatuses. These image sensors convert an optical image focused on the sensors into electrical signals, which represent the intensity of the image. The dynamic range of these imaging devices, however, is often limited due to the relatively low sensitivity of the photosensitive pixels contained in the image sensors.
The dynamic range of an image sensor measures how wide a range of lighting the image sensor can accurately capture. In many natural scenes, the dynamic range often exceeds three orders of magnitude, such as in a scene including a brightly lit section and a section containing shadows. This high dynamic range makes it difficult for the image sensor to accurately capture details of both the brightly lit section and the section containing shadows.
To increase the dynamic range of imaging sensors to capture a subject in low light conditions, the exposure time of the image sensor has been increased. Increasing the exposure time, however, increases the probability that the captured image will be susceptible to shaking of the imaging device. To overcome this problem, techniques in which image signals corresponding to two frames taken during different exposure times are combined to increase dynamic range have been proposed. Conventional techniques, however, require expensive components, complicated processing routines, or both, and are thus associated with relatively high costs.